When and how did the adversarial aspect of the criminal justice system originate, and to what extent is/was it actually adversarial?

Question

As I understand, originally all judicial courts derived their authority from the crown. So too, was the prosecutor in criminal matters referred to as “the crown.” So the crown is both the judge and one of the adversarial sides. So in what sense was the paradigm originally actually “adversarial” in effect?

And how did it develop like this?

And why structure it in this ostensibly even if not “truly” “adversarial” manner? If the crown is supreme (and can apparently be trusted -supposably by itself- to be impartial and exercise judicious restraint) in its judicial capacity while having the final say, then why not allow it simply in its prosecuting capacity to have absolute authority, and why separate “the crown” into these multiple aspects whose purposes are to challenge and sometimes ultimately to overrule and oppose each other?

Answer 1

To answer the history question:

The adversarial system we use today in england-and-wales is the product of centuries of development of law, politics, religion and bureaucracy.

We label a set of features 'adversarial' to distinguish between that set and a distinct set of features we label 'inquisitorial'. They are different means of 'truth-seeking'.

We used to have other methods of truth-seeking: 'wager of law' (aka 'trial by oath' or 'compurgation'), 'trial by ordeal' and 'trial by battle' (aka 'trial by combat). In those days one function of the court was to decide which system to use.

The importance and functions of the judge, jury, advocates and adversaries in England and Wales (and their antecedent states) have changed over these centuries for a variety of reasons.

The Ohio State Law Journal published an accessible and comprehensive yet concise history (A Brief Survey of the Development of the Adversary System by Professor Stephan Landsman) that I would only copy-paste from to answer the question in depth.

Answer 2

canada

To answer only one of the several questions (questions should only ask one question at a time):

If the crown is supreme (and can apparently be trusted to be impartial and exercise judicious restraint) in its judicial capacity while having the final say, then why not allow it simply in its prosecuting capacity to have absolute authority

The Canadian Charter of Rights and Freedoms, at s. 11(d) grants to any person charged with an offence, the right "to be presumed innocent until proven guilty according to law in a fair and public hearing by an independent and impartial tribunal."

The pre-conditions required for independence and impartiality are found in the judiciary, and not in the legislative or executive branches of government.

An essential component of the judicial independence guaranteed by s. 11(d) is "institutional independence." This requires "judicial control over the administrative decisions that bear directly and immediately on the exercise of the judicial function." See Valente v. The Queen, [1985] 2 S.C.R. 673, paras. 47, 52. The other two core components are security of tenure and financial independence.

Judicial independence has been defined as (ibid., para. 18):

the capacity of the courts to perform their constitutional function free from actual or apparent interference by, and to the extent that it is constitutionally possible, free from actual or apparent dependence upon, any persons or institutions, including, in particular, the executive arm of government, over which they do not exercise direct control.

Conversely, the members of the legislative and executive elements of the Crown do not benefit from the security of tenure, financial independence, and institutional independence that give the public the confidence in the impartiality of the judiciary.